best place to start learning is the FAQ section and the wiki.
your install will be made a little easier because you already have your speakers powered by outboard amplifiers.
your monitors will will work, but there are 2 problems with them that make them generally undesirable in a carPC system. I assume they are both low resolution composite video monitors. when hooked up to a computer; composite monitors display burry/fuzzy and sometimes unreadable text (depending on the font and font size). large button/text front ends can help with this but the picture will still be inferior when compared to VGA monitors. this FAQ helps explain it in greater detail.
the other problem with your monitors is the lack of a [usable] touchscreen. even if they have a touchscreen, you won't be able to use it for your carPC (unless you hack the monitor apart and install a new touchscreen/controller with USB interface).
as for motherboard recommendations, it depends on what you want out of your carPC. if you only want it play music and videos, then almost anything will do. if you want more out it then list what type of programs you plan to run and what hardware features you would like it to have.
BTW, welcome to carPC'ing!